In the case of deterioration caused by corrosion expansion of reinforcing bars such as salt damage, large damages cannot be found on the concrete surface until cracking. In order to estimate the progress of salt damage, the authors have been investigating to estimate content of chloride ions using electromagnetic waves, which is one of the nondestructive testing methods, and have found the applicability. On the other hand, the estimation of content of chloride ions using electromagnetic waves is the average content of chloride ions from concrete surface to rebar, and in order to estimate the distribution of content of chloride ions, it is necessary to decide the surface content of chloride ions and the diffusion coefficient which are set to be equivalent to the average content of chloride ions estimated by electromagnetic waves. In this paper, in order to evaluate the distribution of content of chloride ions during the latency stage and the progression stage before corrosion induced cracks appear on the concrete surface, the method to estimate the distribution of content of chloride ions in the cover concrete combining both electromagnetic waves and X-ray fluorescent is proposed.